(221) Adjuvant Radiation Therapy and Mortality in Older Women with Early-Stage Endometrial Cancer: An Analysis Using The SEER-Medicare Linkage

Publication Number: 895

Background: Endometrial cancer (EC) is the sixth most commonly diagnosed cancer among women worldwide, and with a median age of 62 at diagnosis, it affects a significant number of older women. With increases in obesity prevalence and an aging population, there is an anticipated increase in EC diagnosis in older women. Currently, there is insufficient evidence to reliably support whether older women with early-stage EC derive clinically meaningful survival benefit from adjuvant radiation therapy.

Objectives: To assess mortality outcomes associated with adjuvant radiation therapy among older women with early-stage EC who underwent hysterectomy.

Methods: Using data from the Surveillance Epidemiology and End Results cancer registry program and the Medicare claims linkage, we identified women (aged ≥66 years) diagnosed with first primary stage I-II EC during 2004-2016 who underwent a hysterectomy in the 4-months following diagnosis. Women were eligible if they had continuous Medicare coverage at least one-year pre-hysterectomy and 7 months post-hysterectomy. Diagnosis and procedure codes were used to identify radiation claims filed for the 7-months post-hysterectomy. All-cause- and EC-specific mortality risks were compared across treatment groups: hysterectomy alone, hysterectomy+external beam radiation therapy (EBRT), hysterectomy+vaginal brachytherapy (VBT), or hysterectomy+VBT+EBRT. Cox proportional hazard regression was used to estimate mortality hazard ratios (HRs) and 95% CIs comparing treatment groups after accounting for measured confounders using propensity score weighting.

Results: A total of 19,880 women were included. During a median follow-up of 5.9 years (interquartile range, IQR=3.2-9.3), there were 5,545 all-cause deaths and 1,006 disease-specific deaths. Compared to women treated with hysterectomy alone, women treated with hysterectomy+VBT had reduced all-cause mortality (HR=0.84; 95% CI=0.77-0.93) and EC-specific mortality (HR=0.69; 95% CI=0.54-0.88). Among women treated with any radiation therapy, women treated with hysterectomy+VBT+EBRT had increased all-cause mortality (HR=1.14; 95% CI=1.01-1.28) and EC-specific mortality (HR=1.37; 95% CI=1.05-1.79) compared to women treated with hysterectomy+VBT.

Conclusions: Our results, based on a national data resource, support findings from clinical trials, suggesting that, VBT should be considered as the possible adjuvant treatment of choice for early-stage EC, given the reduced mortality risk. In women who require the use of adjuvant radiation, the addition of EBRT to VBT was associated with increased mortality risk, however more detailed clinical data are needed to consider this association carefully, as this may reflect underlying severity of the disease.